Bladder cancer is the fourth most common cancer in men and ninth in women (Jemal, et al., Cancer J Clin, (2008) 58: 71-96). At diagnosis, about 75% of patients are at the non-invasive stages (Fleming, et al., AJCC (American Joint Committee on Cancer) Cancer Staging Manuel, 5th ed., 5th edition. Philadelphia: Lippincott-Raven, 1997). The treatment is usually by transurethral resection of bladder tumor (TURBT) followed by intravesical instillation of Bacillus Calmette-Guerin (BCG) or mitomycin C to reduce recurrence. Despite this treatment, 20-80% of patients will recur and 25% will have disease progression (Herr, et al., J Clin Oncol, (1995) 13: 1404-1408; Herr, et al., J Urol, (1989) 141: 22-29; and Cookson, et al., J Urol, (1997) 158: 62-67). All these patients require long-term follow-up with urine cytology and cystoscopy. The sensitivity of urine cytology ranges between 29-74%, with the overall sensitivity of approximately 35% (Eissa, et al., Curr Opin Obstet Gynecol, (2003) 15: 395-403; van Rhijn, et al., Eur Urol, (2005) 47: 736-748; and Lotan, et al., Urology, (2003) 61: 109-118). Cystoscopy is intrusive, uncomfortable and costly. Because of the long-term survival and the need for lifelong monitoring, the cost per case for bladder cancer is the highest among all cancer types, ranging from $96,000-$187,000 (2001 values) per case (Riley, et al., Med Care, (1995) 33: 828-841; Botteman, et al., Pharmacoeconomics, (2003) 21: 1315-1330).
The present invention is based, in part, on the use of combinatorial chemistry technology to develop bladder cancer-specific ligands for imaging and targeted therapy during the diagnosis, treatment and follow-up of bladder cancer. One-bead one-compound combinatorial peptide library technology (OBOC) (Lam, et al., Nature, (1991) 354: 82-84, 1991; and Lam, et al., Chem Rev, (1997) 97: 411-448) was used to identify bladder cancer specific ligands. When a “split-mix” synthesis method is performed to construct the combinatorial library, random libraries of millions of beads (90 μm in diameter) are generated. Each bead bears up to 1013 copies of ligands with the same amino acid sequences. At each round of screening, millions of library beads (ligands) can be screened in parallel for specific targets (receptor, antibody, enzyme, virus and whole cell, etc). Positive beads that bear peptides specific for the targets can be identified using an enzyme-linked colorimetric assay similar to the western blot, or by the evidence of cell attachment on the bead surface (Songyang, et al., J Biol Chem, (1995) 270: 14863-14866; and Liu, et al., J Am Chem Soc, (2002) 124: 7678-7680). Unnatural amino acids, D-amino acids or even non-peptide moieties can be incorporated in the library to make the molecules resistant to proteolysis and increase the binding affinity. The ligand leads identified through screening of OBOC libraries can be further optimized to generate cancer-specific ligands with high affinity and specificity (Peng, et al., Nat Chem Biol, (2006) 2: 381-389).